Aim of this study is to develop an accurate and reliable method for estimating propagation characteristics inside and outside aircraft cabin so as to advance wireless link design for Wireless Avionics Intra-Communication (WAIC) system. This paper estimates propagation characteristics from inside cabin to exterior mounted antenna of WAIC system installed on a passenger aircraft (Airbus 320-200 model). EMF distributions excited by a 4.4 GHz wireless transmitter inside cabin are analyzed and fundamental characteristics for the WAIC system are derived from the analysis results.